the "KITES ON AIR" group
|SAN DIEGO, CALIFORNIA USA
Several of our kite-antenna designs are fed
from the ground using long lengths of coaxial
cable. Therefore, the cable is a very important
part of our antenna design. We can choose
from three different cable types depending on
the particular application. These cables are
RG-8x, RG-58 and 1855A. 100 foot lengths of
each of these cables have been wound onto
plastic reels for easy storage and deployment.
This allows us to conveniently select any of
these cable for use with any of our
kite-antennas. The key parameters of these
three cable types that apply to their use with our
kite-antennas are weight, impedance, losses,
power handling and pull strength. These
specifications are listed in the table below. Since
the lightest qualified cable allows us to reach the
greatest kite-antenna height, we usually choose
either the RG-58/U or 1855A coaxial cable.
COAXIAL CABLE FEED LINES
CABLE TYPE WEIGHT PER 100 FT IMPEDANCE LOSSES AT 7 mHZ POWER HANDLING PULL STRENGTH
RG-8x 3.7 pounds 50 ohms 0.90 dB per 100 ft 740 watts 75.0 pounds
RG-58/U 2.0 pounds 50 ohms 1.20 dB per 100 ft 1,115 watts 12.4 pounds
1855A 1.7 pounds 75 ohms 1.08 db per 100 ft 500 watts (*) 40.0 pounds
Some of these specifications do not seem to be self consistent. However, they are the values published by the manufacturer.
(*) This is our calculation for power handling based on the center conductor wire size and braid resistance.
SOME ADDITIONAL CABLE INFORMATION
The coaxial cable that connects from the kite-antenna in the air to the radio on the ground serves three
purposes. In addition to carrying the transmitted and received signals, this cable also is used to (1)
discharge to ground any static voltage that could build up on the antenna and (2) provide a back up tether
for the kite in the event that the main fly line breaks or becomes disconnected from the fly line
For most of our antenna designs, the cable drops straight down from the kite to the ground directly below
the kite. Sometimes, we have found it better to dress the feed line cable back along the kite's fly line. In
either case, any surplus cable rests on the ground below the kite. Because coaxial cable is used, there is
no change in transmission line characteristics whether the cable is in the air or on the ground.
We also recommend considering soldered connectors rather than crimped connectors on the ends of the
coaxial cables for best pulling strength if it is needed as a “catch” line should the main fly break or become
disconnected while the kite is in the air.
OUR COAXIAL CABLE EVALUATION AND SELECTION HISTORY
In the beginning, we used RG-8x to feed our kite-antennas because this was the lightest cable that we had
on hand. Although this cable worked fine for our first kite-antennas which were carried aboard or
suspended below a large 12 foot delta kite, a relatively strong wind was needed to lift the delta to the height
that we wanted.
Next, we spliced a number of RG-58/U cables together to created a cable that was substantially lighter than
our original RG-8x cable. This allowed much higher kite-antenna heights to be achieved even when we used
smaller kites for lifting or were operating when the winds were lighter. The slight increase in power loss when
using the RG-58/U cable was easily compensated for by the higher kite flying heights that we got with same
lifting kites and winds. This cable soon became our cable of choice.
Our next cable breakthrough occurred when one of our group members, Bob (KG6EJW) came up with a
length of 1855A video cable. This cable weighs 1.7 pounds per 100 feet and provided more than 50%
weight saving compared to RG-8x cable. Although this cable does not have an "official" RF power rating, we
made our own power calculations based on the center conductor wire size. We came up with an estimated
continuous RF power rating of 500 watts. This power handling ability is suitable for any of the radios that we
use to power our kite-antennas. Needless to day, this cable has now become one of our favorites. It is nice
to see our kite-antennas flying at up to 100 feet of height, even on days when the winds are moderate.
RG-8x RG-58/U 1855A
Last updated August 6, 2017
To store and to make long lengths of
coaxial cables easy to use at the kite
"Christmas light" reels. Several 125 foot
lengths of cable travel with us whenever
we go kite flying. This length is chosen
since it lets us fly our half wave dipole
kites at heights of 100 feet or more while
limiting the cable losses to less than 2 dB.
This cable loss is more thancompensated
for by the improved signal strength that
we get with the increased kite-antenna
At least 200 feet of RG-58/U size cable
can be wound onto the reel shown which
costs about $12 on Amazon.
We are also planning to evaluate RG-174/U coaxial cable (pictured below) for use with our kite antennas.
This cable is only 0.11 inches in diameter and weighs in at only 0.8 pounds per 100 feet. This cable should
easily carry as much as 350 watts of power with losses in the order of 3 db or less per 100 feet at 7 MHz.
The expectation is that these higher losses, relative to RG-59/U, will be more than compensated for by the
higher kite-antenna height that can be achieved with this lighter RG-174/U cable.
A super light weight 20 meter vertical dipole kite-antenna is presently being fabricated that will take
advantage of the light weight of RG-174/U coaxial cable. Our current center fed dipole design, complete
with a current choke, weighs in at only 3 ounces. This dipole antenna will be fed using a 100 foot length of
RG-174/U coax which will comprise the "airborne" portion of the antenna's coax cable feed line. With this
cable (which will weigh only 12.5 ounces) the total weight that will have to be lifted by the kite will only be
about one pound. An additional, 100 feet of RG-58/U or RG-8x will added to the end of the RG-174/U which
will lay on the ground and connect back to the radio. The RF loss for this super light weight antenna will be
about 2 db greater than the present design but the airborne weight will only be about half of our previous
design. For a typical 10 db over S9 signal, the signal for this new ultra light weight antenna should still be 8
db over S9 - hardly a noticeable reduction in signal!
A NEW ULTRA LIGHT WEIGHT HALF WAVE CENTER FED VERTICAL DIPOLE KITE-ANTENNA DESIGN